1. Field
A lithium secondary battery is disclosed.
2. Description of the Related Art
A non-aqueous lithium secondary battery typically includes a separator made of a porous insulating film, interposed between positive and negative electrodes, and the pores of the film are impregnated by an electrolyte including a lithium salt dissolved therein. The non-aqueous lithium secondary battery has excellent initial high-capacity and high energy density characteristics. However, when the positive and negative electrodes therein are repetitively contracted and expanded during the charge and discharge cycles and, thus, react with a separator or an electrolyte, the non-aqueous lithium secondary battery may be easily deteriorated, which may result in internal and external short circuits and rapid increases in the temperature of the battery. When the temperature of the battery rapidly increases as aforementioned, the separator fuses and is rapidly contracted or destroyed and, thus, can be short-circuited again.
In order to prevent this problem, separators are formed of a porous polyethylene film having excellent shutdown characteristics, easy handling, and low cost. In those cases, however, the shutdown results in a separator that is partly fused and thus, closes pores and cuts off the current, when the temperature of the battery increases due to overcharge, external or internal short circuit, and the like.
In addition, an attempt has been made to improve safety of the non-aqueous lithium secondary battery by improving heat resistance of an electrode material for a separator and the like and in particular, to secure safety even when a separator therein is sharply contracted or destroyed.